Detailing in Layout ModeKeyCreator \ Layout \ Overview \ Detailing-in-Layout-Mode
You can detail both instance and layout-specific entities. However, some combinations can affect association; see Associativity for more information.
NOTE: When dimensioning an entity that is tagged to an instance, the dimension will assume the instance scale. For instance, placing a 1" line in an instance scaled at 50% (and tagging it to the instance) will result in a dimension of .5".